1. Field of the Invention
This invention relates generally to a method of matching the coefficient of thermal expansion of a plurality of structural members in an optical assembly and, more particularly, to a method of providing a thin spacer element at the end of one or more composite structural members associated with a laser optical assembly, where the combination of the coefficient of thermal expansion of the spacer element and the coefficient of thermal expansion of the structural member matches the coefficient of thermal expansion of a target structural member.
2. Discussion of the Related Art
Laser systems include structural elements that hold and mount optical components, such as mirrors, lenses, etc., in precise alignment with each other for proper laser operation. For example, certain laser systems include a resonant optical cavity where opposing mirrors are mounted to end plates of the cavity in very precise alignment with each other to maintain the lasing process. The laser system may be subjected to various disturbances, such as g-loads, shock, vibration and acoustical loads. These disturbances may act to misalign the optical components, thus degrading the operation of the laser system. Thus, the structural elements need to be rigid enough to prevent misalignment of the optical components under these disturbances.
In addition to the various disturbances mentioned above, environmental heat or heat caused by the operating temperature of the laser system can also cause misalignment of the optical components. Thermally induced misalignment is caused by certain structural support members associated with the laser system expanding at different rates in response to the heat. This thermal induced misalignment can be the result of the structural members having different lengths, the structural members having the same length but different coefficients of thermal expansion (CTE), or a combination of both. In one laser system, the end plates of the resonant cavity are connected together by four separate structural support members. If the CTE of the structural members are not matched, the heat may cause one member to expand in length more than the others. This length mismatch induces a tilt on the mirrors, which can cause optical misalignment, thus degrading the laser performance.
For those laser systems that need to be light-weight, for example, laser systems used in missile guidance systems on aircraft, the structural members are typically made of composite materials, such as carbon and graphite, to meet the weight requirements. The composite structural members must meet stringent coefficient of thermal expansion requirements for proper laser operation. The CTE of a composite structural member is controlled by material selection (fiber/resin system) and ply orientation. Presently, these types of composite structural members are made by wrapping a ply layer made of the composite material around a suitable substrate. The orientation of the fibers in the ply layer determine the CTE of the resulting member, and thus the ply layer must be accurately wound to meet the CTE tolerances of the laser system. The present manufacturing processes of these types of composite structural members for optical assemblies can not ensure proper orientation of the material to the degree required to meet CTE requirements, which are dictated by optical alignment requirements. Therefore, those structural members that do not meet the proper CTE requirements are discarded, thus incurring waste.
What is needed is a technique for controlling the CTE of composite structural members used to support optical components in a laser system. It is therefore an object of the present invention to provide such a technique.